(1) Field of the Invention
The invention relates to an electrochemical cell for the production of halogenated hydrocarbons and an aqueous solution of an alkali metal hydroxide. In electrochemical cells the free energy of reaction is reduced by the addition of an unsaturated hydrocarbon which results in a reduction in energy consumption while the main product of value is produced.
(2) Description of the Prior Art
Very little work has been reported on halogenation of hydrocarbons in electrochemical systems. Langer et al in the Journal of The Electrochemical Society, 117, No. 4 510 (1970) disclose the electrochemical chlorination of an olefin utilizing an aqueous potassium chloride electrolyte; the reaction taking place on catalytic electrodes. Chlorine is reduced at the cathode to form chloride ions while electrons are supplied by the external circuit. At the anode, the olefin reacts with the chloride ions which are transported from the cathode through the electrolyte to the anode where the chlorinated olefin product is formed with a yield of electrons to the external circuit. At low anode potential (low current), the current yield of dichloroethane (1,2-dichloroethane) was about 90 percent with 10 percent of the current resulting in the formation of chlorohydrin. A yield of dichloropropane utilizing propylene as a feed gas was reported at a current yield of 18 percent.
The early U.S. Pats. of McElroy, U.S. Pat. Nos. 1,253,615; 1,253,616; and 1,253,617; U.S. Pat. No. 1,264,536; U.S. Pat. No. 1,295,339; and U.S. Pat. No. 1,308,797 disclose an electrochemical method for the manufacture of alkali and by products chloroethanol and dichloroethane. An aqueous solution of potassium chloride or sodium chloride is electrolized by McElroy by applying a potential of 3.5 to 5 volts across wire gauze electrodes while the anode is contacted with an olefin. The olefin is chlorinated at the anode, the chlorination reaction serving to depolarize the anode thus resulting in an energy saving over a simple electrolysis process. Platinum black was found to catalyze the chlorination process and lower temperatures were found to favor the formation of 1,2-dichloroethane.
Bhattacharyya et al in the J. Sci. Ind. Res. (India), 11.B 371 (1952) report the results of the use of porous carbon anodes and copper cathodes in a 10 percent sodium chloride electrolyte for the production of 2-chlorethanol with a 5 percent ethylene glycol byproduct. At 90 degrees centigrade the current efficiency for the production of 2-chloroethanol was 1 percent while the current efficiency for the production of ethylene glycol was 17 percent. The current efficiency (yield) at 1 degree centigrade and 22.5 ma/cm.sup.2 was reported as 84 percent for 2-chloroethyanol and 5 percent for ethylene glycol.
Kalinin et al in the Journal of Applied Chemistry (USSR), 19, 1045 (1946) disclose the aqueous electrochemical chlorination of ethylene utilizing aqueous sodium chloride as an electrolyte and graphite electrodes. A yield of 1,2-dichloroethane of 44 percent utilizing a five normal solution of sodium chloride is reported.
Simmrock et al in U.S. Pat. No. 4,119,507 disclose an electrochemical system for reacting a chlorine-containing anolyte to form an olefin chlorohydrin which is subsequently reacted to form an oxirane. Low yields of 1,2-dichloropropane are disclosed in the examples; the yields ranging from 7 to 22 percent at a current efficiency of about 99 percent.
In U.S. Pat. No. 4,334,967, a method for preparing 1,2-dichloroethane is disclosed comprising the electrolysis of a 12 to 36 percent aqueous solution of hydrochloric acid at a temperature of 45 to 70 degrees centigrade; ethylene being simultaneously supplied into the anodic space of an electrolytic cell; the electrolyte being previously treated with a metal of the group of iron or compound of a metal of said group.
The major proportion of the vast amounts of energy consumed in the world today is obtained from chemical reactions associated with the thermocombustion of fuels. Production of electrical energy by thermocombustion is restricted by Carnot cycle factors which limit conversion efficiencies to about 40 percent at a central power generation site. The inherently greater efficiency of direct electrical energy generation from electrochemical reaction in fuel cells was recognized around the turn of the century but did not deter the proliferation of mechanical devices as the principal means for electrical energy generation. With the end of the plentiful supply of liquid fossil fuels in sight together with the increase of prices of such fuels subsequent to 1973, fuel cell electrical energy generation is being actively examined.
Many chemical reactions other than combustion release large amounts of energy which are regularly wasted as heat during industrial chemical processing. One means of recovering this energy is the performance of certain reactions at depolarized electrodes. The depolarization process has been defined as one in which favorable thermodynamic factors drive an electrochemical cell in which reactions take place to give a desired chemical product at a reduced electrical energy outlay. The depolarization mode is characterized by reduced electric energy consumption while the main product of value is produced.